Why Do Mosquito Bites Itch?

The itchy welt that forms after a mosquito bite is caused by saliva that the mosquito injects into the skin. When a mosquito bites, it pokes through the skin with six straws like part of its mouth. These are called stylets. At the same time, the mosquito injects saliva into the wound. The saliva keeps the blood from thickening, and makes it easy to suck out.

Most people are allergic to the saliva. It causes the bite to swell and itch. Only female mosquitoes bite — not males. The females need the blood to help develop the eggs inside their bodies.

While you might not immediately realize when you’ve been “bitten” by a mosquito, your bodys immune system is fully aware of what’s going on. It detects the presence of the mosquito saliva and tells your body to produce a substance called histamine to fight it. When the histamine reaches the area of skin where the mosquito “bit” you, it causes blood vessels in the area to swell. That’s why you usually see a mosquito “bite” as a red bump on your skin.

When the blood vessels swell, they also cause nerves in the area to become irritated. Your body feels this nerve irritation as an itching sensation. The histamine response is much like any other type of allergy response you may have experienced in the past. Mosquito bites can be a serious matter.

Even though mosquito bites aren’t always dangerous, they can be and should be avoided as much as possible. Mosquitoes are most active during the hours just before and after sunrise and sundown. During these times, be sure to use bug spray and wear long clothing, if appropriate.

Content for this question contributed by Danny Goldstein, resident of Aptos, Santa Cruz County, California, USA